In the manufacture of nuclear fuel for use in fuel bundles which are incorporated into the nuclear reactors, it is important to employ fuel pellets which have uniform diameter both individually and with respect to the other fuel pellets so that the calculated power requirements and usage of the fuel bundles will be in accordance with prescribed performance standards. Thus, in the fuel bundle each of the rods containing fuel pellets of non-uniform diameter or at least diameters which vary beyond permissible limits, the amount of power produced may not be in accord with specified power ratings for fuel of a certain diameter. This will cause a difference in the life of the particular fuel rod supplying the power as well as with respect to the power curve over the life of the fuel. Thus, it is clear that it is important to make sure that the diameters of the pellets are within a permissible tolerance.
Heretofore, a technique commonly used to measure diameters of pellets and diameter profiles of a single pellet comprise an electro-mechanical system. This system uses a linear variable displacement transformer (LVDT) to make a one point measurement of the pellet diameter. Because the measurement has to be made with the pellet stationary, the system throughput is low. The system also has the disadvantage in that only a one point measurement is made.
It is important in measurement of diameters and numerous objects such as nuclear fuel pellets to have a system which measures the parameter of the pellet without the necessity of contacting the pellet, which can cause possible scratching that would result in an unsatisfactory appearance and in some cases the scratches would destroy the dimensional requirements. Further, it is important that the system provide a measurement which is very accurate and also which can provide a complete diameter profile so that various dimensional anomalies can be quickly ascertained from a suitable strip chart recording of the diameter profile of each pellet. Finally, it is important that the system be relatively inexpensive and of course reliable.
Other prior art which has been considered in connection with the subject invention include the following patents: U.S. Pat. Nos. 2,730,006 3,549,896 2,931,917 3,566,135 2,941,087 3,712,741 3,204,109 3,730,633 3,365,699 3,737,856 3,454,759.